The present invention relates to bone plates, more particularly the present invention relates to bone plates that apply compressive stress over a fracture. Most particularly, the present invention relates to bone plates that provide incremental compressive stress over a fracture.
Fasteners that thread into the vertebra are known, such fasteners, their structures and the manner in which they are used are taught in such prior art patents as U.S. Pat. No. 4,696,290 to Steffee; and U.S. Pat. No. 4,854,311 to Steffee; U.S. Pat. No. 5,613,967 to Engelhardt et al.; and U.S. Pat. No. 5,261,910 to Warden et al. and are incorporated herein by reference.
According to the present invention a bone plate apparatus is provided that preloads or provides incremental compressive stress over a fracture to aid in fusion. The plate apparatus includes a plate that is formed with spaced-apart slots and rims extending about the perimeter of each of the slots. The rim includes opposite interrupted surfaces extending along the lengths of the slots. In addition, the plate apparatus includes fasteners that are formed to be coupled to plate. Each fastener includes a shaft that extends into a vertebra, a collar coupled to shaft and formed to engage the plate, and a head that is sized for extension through the respective slot. The collar of the fastener includes an interrupted surface that is formed to mate with the interrupted surface of the rim of the plate. Nuts are also provided to cooperate with the heads of the fasteners to couple the interrupted surfaces of the fastener and rim together. Thus, the plate is prevented from moving relative to the vertebrae and the fasteners.
In preferred embodiments, the slots include a first end and a second end and the rims extend between the first and second ends. Each rim includes opposite ends adjacent to the first and second ends of the slots and side walls that extend between the opposite ends of the rim. The interrupted surface is formed on each of the side walls of the rim to mate with the interrupted surface formed on the collar of the fastener. The interruptions on the plate and fastener are preferably teeth that have a width of about 1 mm. In addition to spaced apart teeth providing the interruptions, it will be apparent that the interruptions made take the form of spaced apart bumps or indents that mate with corresponding spaced apart recesses. In this application and in the claims, therefore the term "interruptions" is intended to refer to spaced apart elements or recessed on the slots that mate or mesh with spaced apart elements or recesses on the fastener or locking device for fastener.
Therefore, according to the present invention a spinal plate assembly is provided that includes a plate having at least two elongated slots, a threaded fastener to extend through each slot into the spine, and a locking device to engage each fastener to hold it in a selected position in its slot. Each slot is formed with interruptions spaced along its length. In addition, cooperating interruptions are formed on the fastener or the locking device to mate with the slot's interruptions selectively to position the plate relative to the fastener.
Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.